Contoured Molten Metal Filter Cups

ABSTRACT

Contoured molten metal filter cups having an interstitial flow space that is maintained between the inner-wall of a molten metal pouring cone, riser sleeve or mold and the outer wall of the filter cup are disclosed. The interstitial space provided by the contoured filter cups results in significantly increased molten metal throughput during casting operations, while simultaneously providing an increased level of filtering efficiency.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/164,150 filed Mar. 27, 2009, which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to filters for molten metal, and more particularly to contoured molten metal filter cups.

BACKGROUND INFORMATION

Investment casting foundries utilize pouring cones as a core components of an investment casting tree, while other metalcasting foundries employ a wide variety of mold designs that include green sand, no-bake, permanent mold, and other materials in both horizontal and vertically-parted configurations. In various metalcasting techniques, there are advantages to filtering out slag and dross that form in the molten metal during pouring. Metalcasting foundries currently use different kinds of molten metal filter media, including ceramic foam filters, ceramic cellular filters, extruded lattice filters, and both fiberglass and silica mesh filter cups.

Molten metal filter cups produced from fiberglass, silica mesh or other materials have usually been designed to fit tightly against or conform as close as possible to the inner walls of the molten metal casting structures in which they are placed, such as investment casting ceramic pour cones, runner sections within a mold, and riser sleeves. The rationale behind this technique is to ensure that the cup remains stable during pouring of the molten metal. Examples of silica mesh filter cups are described in U.S. Application Publication No. 2008/0173591, which is incorporated herein by reference.

While the primary purpose of using filter cups within metal casting structures is to filter out the slag and dross, another important performance characteristic of metalcasting operations is the molten metal flow rate through the filter cups, typically referred to as “throughput”. Conventionally, the throughput of molten metal poured through filter cups or other filter media is increased or decreased by varying the size of the fabric mesh holes of the filter cups, with a larger mesh size (larger holes) providing higher throughput, and a smaller mesh size providing lower throughput. Users of ceramic filters would increase or decrease the pore size of their filter material to manipulate the throughput rate in the same manner. Unfortunately, the tradeoff for increased throughput comes at the cost of a potential reduction in filtering efficiency. While larger meshes or pore sizes permit more metal to flow through at faster rates, they also allow additional slag and dross to pass as well.

SUMMARY OF THE INVENTION

The present invention provides contoured molten metal filter cups having an interstitial flow space that is maintained between the inner-wall of a metalcasting structure such as a ceramic pouring cone, mold pattern, riser sleeve and the like, and the outer-wall of the filter cup. Examples of metal casting structures also include the contact area within or used as part of any variety of metalcasting mold patterns such as green sand, no-bake, permanent mold, horizontal and vertically parted molds, and automated pouring systems such as DISAMATIC, Hunter machines, and high and low pressure die-casting machines. The interstitial space provided by the contoured filter cups results in significantly increased molten metal throughput during casting operations, while simultaneously providing an increased level of filtering efficiency.

An aspect of the present invention is to provide a molten metal filter cup comprising an upper wall section having an outer surface structured and arranged to contact an inner surface of a molten metal casting structure, a generally conical lower wall section below the upper wall section structured and arranged to be spaced an offset distance from the inner surface of the molten metal casting structure when the outer surface of the upper wall section contacts the inner surface of the molten metal casting structure, and a bottom below the lower wall section.

Another aspect of the present invention is to provide a molten metal filter cup comprising a generally conical upper wall section, a lower wall section, a transition between the upper and lower wall sections that extends radially inwardly from a lowermost portion of the upper wall section toward an uppermost portion of the lower wall section, and a bottom below the lower wall section.

A further aspect of the present invention is to provide a molten metal filter cup comprising a generally conical upper wall section, a generally conical lower wall section, and a transition between the upper and lower wall sections that extends radially inwardly from a lowermost portion of the upper wall section toward an uppermost portion of the lower wall section.

These and other aspects of the present invention will be more apparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side sectional view of a contoured molten metal filter cup installed in a pouring cone in accordance with an embodiment of the invention.

FIG. 2 is a side sectional view showing dimensions of the filter cup of FIG. 1.

FIG. 3 is a side sectional view of a contoured molten metal filter cup in accordance with another embodiment of the invention.

DETAILED DESCRIPTION

In accordance with the present invention, contoured molten metal filter cups with an interstitial flow space between the filter cups and pouring cones or other metalcasting structures in which they are installed mitigate the tradeoff of throughput for filter efficiency by providing a geometry that maintains a set level of filtration efficiency while at the same time increasing the molten metal throughput of the pouring cone/filter cup unit. The interstitial flow space significantly increases the filtration area of the filter cups and increases overall filtration efficiency. The filter cups may be installed in a pouring cone or placed elsewhere within a mold pattern, such as the downsprue of an automated casting machine, e.g., a DISAMATIC, or within riser sleeves. The filter cups may be made from any known material, including silica or fiberglass mesh fabrics as well as ceramic material as is common with ceramic foam, ceramic cellular, and extruded lattice filters. For example, one type of filter cup material for use in accordance with an embodiment of the present invention comprises silica mesh fabric with a refractory coating as disclosed in U.S. Application Publication No. 2008/0173591.

FIG. 1 illustrates a contoured molten metal filter cup 10 installed in a ceramic pouring cone 20. Although a ceramic pouring cone 20 is shown in FIG. 1, it is to be understood that the filter cups of the present invention may be installed in various other types of molten metal casting structures. The filter cup 10 includes an upper rim 11, a conical upper wall section 12, a conical, inwardly offset lower wall section 14, and a bottom 16. The filter cup 10 includes a transition 13 between the upper wall section 12 and the lower wall section 14, and another transition 15 between the lower wall section 14 and the bottom 16. In the embodiment shown in FIG. 1, the conical upper wall section 12, conical lower wall section 14 and conical pouring cone 20 are sloped at substantially the same angle measured from a vertical axial flow direction of the filter cup 10.

In accordance with the present invention, the filter cup 10 has an interstitial flow space 18 representing the volume between the inner surface of the pouring cone 20 and the outer surface of the lower wall section 14. While the upper wall section 12 of the filter cup 10 contacts the inner surface of the pouring cone 20, the lower wall section 14 is located radially inwardly of the pouring cone 20 to provide the interstitial flow space 18.

FIG. 2 illustrates several dimensions of the filter cup 10. The upper rim 11 has an outer diameter OD_(R) and an inner diameter ID_(R). The upper wall section 12 has an outer diameter OD_(U) measured at the lowermost portion of the upper wall section, and a height H_(U). The lower wall section 14 has an outer diameter OD_(L) measured at its uppermost portion, and a height H_(L). The lower wall section 14 has an offset distance D representing the distance between the outer surface of the lower wall section 14 and the inner surface of the pouring cone 20. The conical lower wall section 14 is sloped at an angle A measured from a vertical axial flow direction of the filter cup 10. The bottom 16 has an outer diameter OD_(B) measured at the transition 15 between the lower wall section 14 and the bottom 16. The filter cup 10 has a thickness T.

The dimensions of the filter cup 10 shown in FIG. 2 may be selected depending upon the particular geometry of the pouring cone or other metal casting structure. For example, the outer diameter OD_(R) of the upper rim 11 may typically be from about 4 to about 7 inches, e.g., about 5.5 inches. The inner diameter ID_(R) of the upper rim 11 may typically be from about 2.5 to about 6 inches, e.g., about 3.25 inches. The outer diameter OD_(U) of the upper wall section 12 may be typically from about 2 to about 5 inches, e.g., about 3 inches. The outer diameter OD_(L) of the lower wall section 14 may typically be from about 2.2 to about 5.5 inches, e.g., about 3 inches. The height H_(U) of the upper wall section 12 may typically be from about 0.2 to 1 inch, e.g., about 0.4 inch. The height H_(L) of the lower wall section 14 may typically be from about 0.5 to about 4 inches, e.g., about 2 inches. The offset distance D of the lower wall section 14 may typically be from about 0.1 to about 0.5 inch, e.g., about 0.13 inch. The cone slope angle A of the lower wall section 14 may typically be from about 1 to about 30 degrees, more typically from about 5 to about 20 degrees, e.g., about 15 degrees. The slope angles of the upper wall section 12 and pouring cone 20 may be the same as, or different from, the slope angle A of the lower wall section 14. The diameter OD_(B) of the bottom 16 may typically be from about 1 to about 3 inches, e.g., about 1.5 or 1.6 inches. The thickness T of the filter cup 10 may be typically from about 0.01 to about 0.1 or 0.2 inch, e.g., about 0.04 inch. Although specific dimensional ranges are given above, it is to be understood that the various dimensions may be adjusted as desired, depending upon the particular casting operation and pouring cone or other metal casting structure geometry.

At the top of the pouring cone 20 and filter cup 10, the rim 11 and the upper wall section 12 contact and remain flush against the contour and angle of the inner wall of the ceramic pouring cone 20 to provide a cup weight-bearing area. They continue down to the point where the two are separated from each other at the transition 13. The cavity or space 18 created between the lower wall 14 of the filter cup 10 and the inner surface of the pouring cone 20 provides the interstitial flow space 18, which starts at the end of the cup weight-bearing area (point of separation) and continues downward along the outer surface of the lower wall section 14, following the sloping contour of the pouring cone 20 and ends at the transition 15 at the hemispherical or flat bottom 16 of the filter cup 10.

FIG. 3 illustrates a filter cup 110 in accordance with another embodiment of the present invention, with like reference numerals designating similar elements in both FIGS. 2 and 3. In a particular embodiment, the filter cup 110 shown in FIG. 3 may have an outer rim diameter OD_(R) of about 5.5 inches, an inner rim diameter ID_(R) of about 4 inches, an outer diameter OD_(U) of the upper wall section 12 of about 3.5 to 3.7 inches, an outer diameter OD_(L) of the lower wall section 14 of about 3.3 to 3.5 inches, an upper wall section height H_(U) of about 0.4 inch, and a lower wall section height H_(L) of about 1.4 inches. The diameter OD_(B) of the bottom 16 may be about 2.7 or 2.8 inches. The filter cup thickness T and offset distance D of the interstitial flow space 18 in the embodiment shown in FIG. 3 may be similar to those of the embodiment of FIG. 2.

To confirm the improved throughput of the present filters, tests were conducted using standard investment casting techniques to cast a stainless steel alloy (nickel chrominum Stainless Steel Alloy 625) in multiple runs of 75 pounds each. The same testing parameters and number of iterations were run and data recorded using a conventional filter cup design with no interstitial flow space in comparison with the contoured filter cup design shown in FIG. 2. The average pour time for the conventional filter was 8 seconds, in comparison with an average pour time of 6 seconds for the filter cup design of the present invention. An average throughput increase of 25 percent was thus achieved with the contoured filter cup of the present invention.

The casting test results confirm an average increase in measured molten metal throughput of at least 20 or 25 percent. Further, the effective filtration area in the cup may be increased by over 50 percent, typically over 75 percent, as the molten metal is able to flow through the side walls and into the interstitial flow space, instead of being force-focused at the very bottom of the filter cup as in conventional designs.

Whereas particular embodiments of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims. 

1. A molten metal filter cup comprising: an upper wall section having an outer surface structured and arranged to contact an inner surface of a molten metal casting structure; a generally conical lower wall section below the upper wall section structured and arranged to be spaced an offset distance from the inner surface of the molten metal casting structure when the outer surface of the upper wall section contacts the inner surface of the molten metal casting structure; and a bottom below the lower wall section.
 2. The molten metal filter cup of claim 1, wherein the upper wall section is generally conical.
 3. The molten metal filter cup of claim 2, wherein the upper wall section and lower wall section are sloped at substantially the same angle measured from a vertical axial flow direction of the filter cup.
 4. The molten metal filter cup of claim 3, wherein the molten metal casting structure comprises a pouring cone, and the slope angle of the upper and lower wall sections is substantially the same as a slope angle of the pouring cone.
 5. The molten metal filter cup of claim 1, wherein the lower wall section is sloped at an angle of from about 1 to about 30 degrees measured from a vertical axial flow direction of the filter cup.
 6. The molten metal filter cup of claim 1, wherein the offset distance is from about 0.1 to about 0.4 inch.
 7. The molten metal filter cup of claim 1, wherein the offset distance is from about 0.12 to about 0.2 inch.
 8. The molten metal filter cup of claim 1, wherein the offset distance is substantially constant along a length of the lower wall section.
 9. The molten metal filter cup of claim 1, wherein the upper and lower wall sections are connected by a transition that extends radially inwardly at a lowermost portion of the upper wall.
 10. The molten metal filter cup of claim 9, wherein the transition connecting the upper and lower wall sections extend radially outwardly at an uppermost portion of the lower wall section.
 11. The molten metal filter cup of claim 10, wherein the transition connecting the upper and lower wall sections has an outer surface comprising a convex portion where the transition connects to the upper wall section, and a concave portion where the transition connects to the lower wall section.
 12. The molten metal filter cup of claim 1, further comprising a generally annular upper rim connected to the upper wall section.
 13. The molten metal filter cup of claim 1, wherein the lower wall section has a height measured in a vertical axial flow direction of the filter cup that is at least about 50 percent of an overall height of the filter cup.
 14. The molten metal filter cup of claim 13, wherein the height of the lower wall section is at least about 75 percent of the overall height of the filter cup.
 15. The molten metal filter cup of claim 13, wherein the upper wall section has a height that is less than about 25 percent of the overall height of the filter cup.
 16. The molten metal filter cup of claim 1, wherein the lower wall section has an uppermost portion having a cross-sectional outer diameter, and the upper wall section has a lowermost portion having a cross-sectional outer diameter that is at least about 5 percent larger than the cross-sectional outer diameter of the lower wall section.
 17. The molten metal filter cup of claim 1, wherein the lower wall section and the bottom are connected by a transition having a convex outer surface.
 18. The molten metal filter cup of claim 1, wherein the bottom is generally hemispherical.
 19. The molten metal filter cup of claim 1, wherein the bottom is substantially flat.
 20. A molten metal filter cup comprising: a generally conical upper wall section; a lower wall section; a transition between the upper and lower wall sections that extends radially inwardly from a lowermost portion of the upper wall section toward an uppermost portion of the lower wall section; and a bottom below the lower wall section.
 21. The molten metal filter cup of claim 20, wherein the transition has an outer surface comprising a convex portion where it connects to the upper wall section and a concave portion where it connects to the lower wall section.
 22. The molten metal filter cup of claim 20, wherein the transition extends radially inwardly a distance of at least about 5 percent of a cross-sectional outer diameter of the lowermost portion of the upper wall section.
 23. The molten metal filter cup of claim 22, wherein the radial extension distance is at least about 0.1 inch.
 24. The molten metal filter cup of claim 22, wherein the radial extension distance is from about 0.12 to about 0.2 inch.
 25. The molten metal filter cup of claim 20, wherein the lower wall section is generally conical.
 26. A molten metal filter cup comprising: a generally conical upper wall section; a generally conical lower wall section; and a transition between the upper and lower wall sections that extends radially inwardly from a lowermost portion of the upper wall section toward an uppermost portion of the lower wall section. 